A storage system generally provides a higher-level apparatus (for example, a host computer) with a logical volume, which is created based on a RAID (Redundant Array of Independent Disks) group configured from multiple storage devices. In recent years, a nonvolatile semiconductor storage apparatus comprising multiple nonvolatile chips has been used as the storage device either in addition to or instead of a HDD (Hard Disk Drive). As a nonvolatile semiconductor storage device, for example, a flash memory comprising multiple flash memory chips (hereinafter, FM chip) is used.
Larger capacity and higher performance are required in a storage system equipped with flash memory like this. However, when high-speed processors and flash memory chips are augmented to meet this requirement, there is the likelihood that the power consumption of the storage system as a whole will increase, and that this power consumption will exceed the power capable of being provided by the facility in which the storage system is installed. For this reason, it is necessary to reduce power consumption while realizing increased capacity and higher performance in the storage system, and, for example, technology for computing a number of FM chips, which can be processed in parallel by a controller, which controls the entire storage system, and for a FM chip controller to control the number of FM chips on the basis of the relevant computation result, is disclosed in Patent Literature 1.